The invention concerns a back-washable filter for liquids containing impurities.
A filter of this type having the features A to F of claim 11 is known from DE 91 03 149 U1, in which a circularly cylindrical filter body is located in a circularly cylindrical filter housing, with the filter body separating a inner radial incoming flow chamber on the unfiltered side from an outer radial outgoing flow chamber on the filtered side. An axially extending washing channel is located in the outgoing flow chamber which presses radially outward against the filter body. The washing channel has an axially extending washing gap which faces the filter body. In addition, the washing channel communicates with a cleaning liquid source. The cleaning liquid can be pressurized in the washing channel to achieve efficient cleaning and/or backwashing of the filter body. The filter body and the washing channel can be moved relative to one another in one movement direction. In this way, the entire lateral surface of the filter body can be completely backwashed in the course of a complete rotation of the filter body.
A filter of this type is also known from DE 198 03 083, which is older, but was published later, which also has the features G to J of claim 11 and in which the filter body has links on a side facing the washing channel which are positioned at intervals in the movement direction. Each two neighboring links form a separately back-washable segment on the filter body, with the two associated links pressing tightly against the washing channel before and after the washing opening relative to the movement direction and exposing the washing opening during washing of one of these segments. The extension of each sealing surface is greater than the extension of the washing opening relative to the movement direction.
In filters of this type, the backwashing of the filter body is performed by pressurizing the cleaning liquid in the washing channel, causing the cleaning liquid to penetrate the filter body via the washing gap and remove the dirt on the incoming flow side. The quality of the cleaning effect in these types of filters essentially depends on the liquid volume flow effecting the backwashing. In the known filter, the cleaning liquid in the washing channel is fed to the filter body at an essentially constant pressure, so that the cleaning process can be performed with a correspondingly constant cleaning fluid volume flow. In order for this to be able to be performed continuously along the entire circumference of the filter body, the flow rate of the cleaning agent source, e.g. a pump, must be at least large enough that cleaning liquid can refill the washing channel under pressure with the same volume flow.
A back-washable filter of another type is known from DE 195 23 462 A1 which has a vertically positioned, circularly cylindrical filter housing in which a circularly cylindrical filter body is located which axially separates an incoming flow chamber on the unfiltered side from an outgoing flow chamber on the filtered side. In this filter, a backflow channel is located in the incoming flow chamber and presses against the filter body. This backflow channel has a inlet gap which faces the filter body. The backflow channel communicates with a relatively pressureless outlet, so that backwashing can also be performed in this case. To improve the cleaning effect, the filter body is divided into segments which can have separate flows through them, i.e. can be separately backwashed, and whose curve lengths are at most as long as the curve length of the backflow channel which presses against the outer surface of the filter body. In this case, the filter body is divided into segments by links successively positioned at intervals around the circumference. During washing of the segment, the two associated links press tightly against the backflow channel before and after the supply gap relative to the movement direction, i.e. in the circumferential direction, so that the entire cleaning effect of the backflow channel is limited to the currently activated segment.
The pressure of the cleaning liquid, specifically the filtered side pressure in the outgoing flow chamber during the backwashing process, also remains essentially constant in this filter type, so that a uniform cleaning fluid volume flow can be ensured in this case as well. In order to prevent pressure drop, the volume flow delivered by the cleaning liquid source must be larger than or at least as large as the cleaning liquid volume flow during the backwashing in this case as well. This is provided in this case in that a portion of the filtered liquid is used as the cleaning medium, which is discharged directly from the outgoing flow chamber through the filter body and the backflow channel again. The pump which serves for flow through the filter typically has a pump rate which is many times greater than the backwash volume flow, so that the filter housing cannot be emptied during the backwashing.
The present invention concerns itself with the problem of improving the backwashing effect in a filter of the type initially cited.
This problem is solved by a filter with the features of claim 11.
The invention is based on the general idea of cleaning the individual segments of a segmented filter body one at a time with the aid of a washing procedure acting in a blast-like or pulse-like way, which is achieved with the aid of a cleaning medium store located between the cleaning medium source and the washing opening.
The development of this type of pulse or blast, formed from a relatively large volume flow of cleaning medium at relatively high pressure for backwashing individual segments, is achieved in the filter according to the invention in that the links for separating the segments close the washing opening of the washing channel between two washing procedures. As long as the washing opening is closed, the cleaning medium source can introduce more cleaning medium into the washing channel than exits the channel through the washing opening, so that the possibility exists of producing a pressure increase in the cleaning medium in the washing channel. This increased pressure then causes a washing pulse with increased pressure and elevated volume flow when the washing opening is opened, which significantly improves the cleaning effect.
During the phases in which the links close the washing opening, the cleaning medium store can be filled and pressure can be built up in the cleaning medium in the washing channel and/or in the upstream cleaning medium store. Particularly when the washing channel communicates relatively unrestrictedly with a cleaning medium store, a cleaning medium volume flow can be released for washing when the washing opening is opened which is significantly greater than the delivery flow of the cleaning medium used. Then with, for example, the washing opening being closed at least as long as it is open, a volume can be released during washing which is at least twice as large as the volume fed from the source to the washing channel for filling the store during this time, if the cleaning medium store is permanently fed by the cleaning medium source.
In a special embodiment, the links close the washing opening at least exactly as long as they are opened for cleaning a segment, which allows a particularly high pressure drop and/or volume flow to be achieved.
According to an advantageous embodiment, the washing channel can communicate relatively unrestrictedly with a cleaning medium store, which is downstream from and can be filled by the cleaning medium source, with the cleaning medium able to be pressurized in the cleaning medium store. In an embodiment of this type, the advantages according to the invention are particularly clear, because during the phases in which the links close the washing opening, the cleaning medium store can be filled and pressure in the cleaning medium can be built up in the washing channel and/or in the upstream cleaning medium store. When the washing opening is opened, a cleaning medium volume flow can then be released for washing which is significantly larger than the delivery flow of the cleaning medium source used. Then, for example, with the washing opening being closed at least as long as it is opened, a volume can be released during washing which is at least twice as large as the volume supplied from the source to the washing channel for filling the store during this time, if the cleaning medium store is permanently fed by the cleaning medium source.
This relationship is used in a further development of the filter in that the volume of the cleaning medium store, the washing pressure, and the washing opening are dimensioned in such a way that, during washing of the segment, the cleaning medium volume flow during the entire cleaning procedure is always larger than the filling volume flow of the cleaning medium source. The filter according to the invention differs significantly from typical filters in the clearing effect which can be achieved in this way. In particular, the filter according to the invention does not require a mechanical scraper or stripper to act on the filter body in the incoming flow chamber, which typical filters need for precleaning so that the washing procedure can achieve the desired cleaning effect.
According to a particularly advantageous embodiment, he cleaning medium store can be implemented in the washing channel. For the case in which the filter body is implemented as cylindrical and the flow passes through it from radially outward to radially inward, the washing channel with integrated cleaning medium store is therefore located inside the filter body, so that the assembly dimensions of the filter housing, which is located radially outside, are not changed by these measures. This design is particularly suitable for the usage of a gaseous fluid as the cleaning medium, because it can be particularly easily stored through compression.
A liquid fluid can also be used as the cleaning medium, with an appropriately implemented cleaning medium store then being provided, containing, for example, a gas cushion or a spring-loaded, movable piston for generating a static pretension in the cleaning medium.
In order to implement the closed times of the washing opening as greater than the open times and/or washing times, there is the possibility of implementing the extension of the sealing surfaces of each link in the movement direction as greater than the interval between the sealing surfaces of neighboring links. It has been shown to be particular advantageous to implement the extension of the sealing surfaces as approximately five times larger than the interval between neighboring sealing surfaces.
It is also possible to implement a drive for realizing the relative motion between the filter body and the washing channel in such a way that the relative motion runs more slowly when the sealing surface of a link closes the washing opening and runs more quickly when the washing opening is between the sealing surfaces of neighboring links. It is also possible to use a stepping motor for the drive which, for example, is operated in such a way that it stands longer in a closed position of the washing opening than in an opened position.
Further important features and advantages of the filter according to the invention arise from the sub-claims, the drawings, and the associated description of the figures with reference to the drawings.
It should be noted that the previously described features and the features described in the following are usable not only in the respective combinations indicated, but also in other combinations or alone, without leaving the framework of the present inventon.